netdev - [PATCH net 2/6] net/diag: Warn only once on EMSGSIZE

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Message-Id: <20241106-tcp-md5-diag-prep-v1-2-d62debf3dded@gmail.com>
Date: Wed, 06 Nov 2024 18:10:15 +0000
From: Dmitry Safonov via B4 Relay <devnull+0x7f454c46.gmail.com@...nel.org>
To: "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
 David Ahern <dsahern@...nel.org>, Ivan Delalande <colona@...sta.com>, 
 Matthieu Baerts <matttbe@...nel.org>, Mat Martineau <martineau@...nel.org>, 
 Geliang Tang <geliang@...nel.org>, Boris Pismenny <borisp@...dia.com>, 
 John Fastabend <john.fastabend@...il.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
 mptcp@...ts.linux.dev, Dmitry Safonov <0x7f454c46@...il.com>
Subject: [PATCH net 2/6] net/diag: Warn only once on EMSGSIZE

From: Dmitry Safonov <0x7f454c46@...il.com>

The code clearly expects that the pre-allocated skb will be enough for
the netlink reply message. But if in an unbelievable situation there is
a kernel issue and sk_diag_fill() fails with -EMSGSIZE, this WARN_ON()
can be triggered from userspace. That aggravates the issue from KASLR
leak into possible DOS vector. Use WARN_ON_ONCE() which is clearly
enough to provide an information on a kernel issue.

Signed-off-by: Dmitry Safonov <0x7f454c46@...il.com>
---
 net/ipv4/inet_diag.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/inet_diag.c b/net/ipv4/inet_diag.c
index 67b9cc4c0e47a596a4d588e793b7f13ee040a1e3..ca9a7e61d8d7de80cb234c45c41d6357fde50c11 100644
--- a/net/ipv4/inet_diag.c
+++ b/net/ipv4/inet_diag.c
@@ -583,7 +583,7 @@ int inet_diag_dump_one_icsk(struct inet_hashinfo *hashinfo,

 	err = sk_diag_fill(sk, rep, cb, req, 0, net_admin);
 	if (err < 0) {
-		WARN_ON(err == -EMSGSIZE);
+		WARN_ON_ONCE(err == -EMSGSIZE);
 		nlmsg_free(rep);
 		goto out;
 	}

-- 
2.42.2